Neutrino Emissivity of Dense Stars

The neutrino emissivity of compact stars is investigated in this work. We consider stars consisting of nuclear as well as quark matter for this purpose. Different models are used to calculate the composition of nuclear and quark matter and the neutrino emissivity. Depending on the model under consideration, the neutrino emissivity of nuclear as well as quark matter varies over a wide range. We find that for nuclear matter, the direct URCA processes are allowed for most of the relativistic models without and with strange baryons, whereas for the nonrelativistic models this shows a strong dependence on the type of nuclear interaction employed. When the direct URCA processes are allowed, the neutrino emissivity of hadronic matter is larger than that of the quark matter by several orders of magnitude. We also find that the neutrino emissivity departs from $T^6$ behavior when the temperature is larger than the difference in the Fermi momenta of the particles, participating in the neutrino-producing reactions.Comment: Latex file. 5 figures available on request. accepted in Int. J. Mod. Phys.

Characterization of Jets in Relativistic Heavy Ion Collisions

Jet quenching is considered to be one of the signatures of the formation of quark gluon plasma. In order to investigate the jet quenching, it is necessary to detect jets produced in relativistic heavy ion collisions, determine their properties and compare those with the jets one obtains in hadron-hadron or $e^+-e^-$ collisions. In this work, we propose that calculation of flow parameters may be used to detect and characterize jets in relativistic heavy ion collisions.Comment: 18 pages, 4 figures, more discussions are added, to be published in Phys. Rev.

On the Limitations of Neutrino Emissivity Formula of Iwamoto

The neutrino emissivity from two and three flavour quark matter is numerically calculated and compared with Iwamoto's formula. We find that the calculated emissivity is smaller than Iwamoto's result by orders of magnitude when $p_{f}(u)+p_{f}(e)-p_{f}(d(s))$ is comparable with the temperature. We attribute it to the severe restriction imposed by momentum conservation on the phase space integral. We obtain an alternate formula for the neutrino emissivity which is valid when the quarks and electrons are degenerate and $p_{f}(u)~+~p_{f}(e)~-~p_{f}(d(s))$ is large compared to the temperature.Comment: Latex Version 2.09, 15 pages, 5 postscript figures available upon request, preprint No. IP/BBSR/93-6

Detection of Minimum-Ionizing Particles and Nuclear Counter Effect with Pure BGO and BSO Crystals with Photodiode Read-out

Long BGO (Bismuth Germanate) and BSO (Bismuth Silicate) crystals coupled with silicon photodiodes have been used to detect minimum-ionizing particles(MIP). With a low noise amplifier customized for this purpose, the crystals can detect MIPs with an excellent signal-to-noise ratio. The NCE(Nuclear Counter Effect} is also clearly observed and measured. Effect of full and partial wrapping of a reflector around the crystal on light collection is also studied.Comment: 18 pages, including 5 figures; LaTeX and EP

UHE neutrino damping in a thermal gas of relic neutrinos

We present a calculation of the damping of an ultra-energetic (UHE) cosmic neutrino travelling through the thermal gas of relic neutrinos, using the formalism of finite-temperature field theory. From the self-energy diagram due to Z exchange, we obtain the annihilation cross section for an UHE neutrino interacting with an antineutrino from the background. This method allows us to derive the full expressions for the UHE neutrino transmission probability, taking into account the momentum of relic neutrinos. We compare our results with the approximations in use in the literature. We discuss the effect of thermal motion on the shape of the absorption dips for different UHE neutrino fluxes as well as in the context of relic neutrino clustering. We find that for ratios of the neutrino mass to the relic background temperature $10^2$ or smaller, the thermal broadening of the absorption lines could significantly affect the determination of the neutrino mass and of the characteristics of the population of UHE sources.Comment: 18 pages, 6 figures. Typos corrected. More accurate treatment of the interaction with relic neutrino clusters. Accepted for publication in Astroparticle Physic

Supernova SN 2012dn: A spectroscopic clone of SN 2006gz

We present optical and UV analysis of the luminous type Ia supernova SN 2012dn covering the period $\sim -$11 to +109 days with respect to the $B$ band maximum, that occurred on JD 2456132.89 $\pm$ 0.19, with an apparent magnitude of $m_{B}^\text{max}$ = 14.38 $\pm$ 0.02. The absolute magnitudes at maximum in $B$ and $V$ bands are $M_{B}^\text{max} = -19.52 \pm 0.15$ and $M_{V}^\text{max} = -19.42 \pm 0.15$, respectively. SN 2012dn is marginally luminous compared to normal type Ia supernovae. The peak bolometric luminosity of $\log L_\text{bol}^\text{max} = 43.27 \pm 0.06$ erg s$^{-1}$ suggests that $0.82 \pm 0.12$ M$_\odot$ of $^{56}$Ni was synthesized in the explosion. The decline rate $\Delta m_{15}(B)_\text{true}= 0.92 \pm 0.04$ mag is lower than that of normal type Ia supernovae, and similar to the luminous SN 1991T. However, the photometric and spectroscopic behaviour of SN 2012dn is different from that of SN 1991T. Early phase light curves in $R$ and $I$ bands are very broad. The $I$ band peak has a plateau-like appearance similar to the super-Chandra SN 2009dc. Pre-maximum spectra show clear evidence of C\,{\sc ii} 6580 \AA\, line, indicating the presence of unburned materials. The velocity evolution of C\,{\ sc ii} line is peculiar. Except for the very early phase ($\sim-$13 d), the C\,{\sc ii} line velocity is lower than the velocity estimated using the Si\,{\sc ii} line. During the pre-maximum and close to maximum phase, to reproduce observed shape of the spectra, the synthetic spectrum code {\sc syn++} needs significantly higher blackbody temperature than those required for normal type Ia events. The photospheric velocity evolution and other spectral properties are similar to those of the carbon-rich SN 2006gz.Comment: Accepted for publication in MNRAS, 19 pages, 20 figure